Illumination is indispensable in our everyday life. Commonly, incandescent lamps or fluorescent lamps are used for illuminating. Here we take the fluorescent lamp as an example.
A fluorescent lamp, which is one type of discharge lamps, includes a glass tube and some dischargeable gas, for example, argon and a little mercury vapor contained in the glass tube. Some fluorescent powder is spread on the inner surface of the glass tube. Two electrodes, i.e., an anode and a cathode, are disposed at the two ends of the glass tube. The two electrodes are formed by tungsten filaments. An example of luminescence in a fluorescent lamp is as follows.
A voltage is applied between the two electrodes and an electrical current is formed in the two electrodes. The two electrodes are heated by the electrical current and begin to discharge. Many electrons are generated by the discharging of the electrodes. The electrons move freely in the glass pipe and collide with atoms of the mercury vapor, and ultraviolet radiation is generated due to collisions between the electrons and the atoms of mercury vapor. The ultraviolet radiation excites the fluorescent powder on the inner surface of the glass tube and the fluorescent power generates a visible light.
However, the fluorescent lamp includes mercury vapor, which may cause pollution. The fluorescent lamp thus requires two energy transformation processes to emit light, from electric energy to luminous energy (generation of ultraviolet radiation) and from luminous energy to luminous energy (generation of the visible light by the fluorescent power), which has a low efficiency of energy transformation.
What is needed, therefore, is to provide an illumination device with higher efficiency of energy transformation.